S H 



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DEPARTMENT OF COMMERCE 

BUREAU OF FISHERIES 

HUGH M. SMITH, Commi«8ion«r 



By HARDEN F. TAYLOR 

Assistant for Developing Fisheries and 

for Saving and Use of Fishery Products 

U. S. Bureau of Fisheries 



APPENDIX IV TO THE REPORT OF THE U. S. COMMISSIONER 
OF FISHERIES FOR 1920 




Bur«au of Fisheries Document No. 898 



PRICE, 10 CENTS 

Sold only by the Superintendent of Documents, Government Printing OfiSce 
Washington, D. C 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1921 



DEPARTMENT OF COMMERCE 

'^ BUREAU OF FISHERIES 

HUGH M. SMITH, Commissioner 



PRESERVATION OF FISH NETS 



By HARDEN F. TAYLOR 

Assistant for Developing Fisheries and 

for Saving and Use of Fishery Products 

U. S. Bureau of Fisheries 



APPENDIX IV TO THE REPORT OF THE U. S. COMMISSIONER 
OF FISHERIES FOR 1920 




Bureau of Fisheries Document No. 898 



PRICE, 10 CENTS 

Sold only by the Superintendent of Documents, Government Printing OflSce 
Washington, D. C. 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1921 




CONTENTS. 



Page 

Introduction 3 

Nature of disintegration of nets 3 

Afechanical wear and tear 3 

Bacterial decomposition 4 

Oxidation 5 

Coloring of nets 6 

Preservation of nets by tanning materials 7 

Cold tanning 7 

Hot tanning 7 

Chemistry of tanning materials 8 

Tanning materials used for fish nets 12 

Fixing or mordanting of tanned nets 13 

Cunningham's experiments 13 

Lindeman's experiments 15 

Bull's experiments 19 

Improved recipe for tanning nets 22 

Summary of methods of preservation of nets by tanning 24 

Preservation of nets by methods not dependent on tanning materials 25 

Linseed oil 25 

Tar 26 

Cunningham's further experiments 28 

Preparation of samples 28 

Shrinkage caused by preserving 29 

Creosote, smoke, etc 30 

Copper sulphate 31 

General comments 33 

Care of nets 33 

Conclusion 34 

Citation of literature 34 



2 



LIBRARY OF CONGRESS 
i DOCUMENTS UiV.SION 



PRESERVATION OF FISH NETS. 



By Harden F. Taylor, Assistant for Developing Fisheries and for Saving and 
Use of Fishery Products, U. S. Bureau of Fisheries. 



Contribution from tlie Fishery Products Laboratory, Washington, D. C. 



INTRODUCTION. 

The art of net preservation grew up long ago, as it might be 
expected inevitably to do, where it was necessary to make fishing gear 
of nonliving plant fibers that are exposed to the destructive effects 
of water, air, and sunlight. The word " art " of net preservation as 
distinguished from " science " of net preservation is used advisedly ; 
one needs to see only the multiplicity of recipes for curing or preserv- 
ing nets to be convinced that the processes belong to the same class 
as cookery or home treatment of diseases, where each locality and 
often each family has its own recipes or formulas, which are tena- 
ciously adhered to and believed in. The many recipes found in the 
literature represent the fisherman's efforts to make his expense and 
labor count for more by prolonging the life of the net and reducing 
his overhead expenses. 

The purpose of this paper is not to collect all these old recipes for 
preserving nets, but rather to review the literature of the subject and 
to ]3resent the fundamental principles in the light of chemistry so far 
as they are known, and to give for use those recipes which, from a 
chemical standpoint, seem best calculated to serve their purpose. It 
will be seen that while many methods as practiced are empirical and 
crude, they nevertheless contain the germ of correct chemistry, and 
not a little progress has been made in improvement of technique by 
chemists, notably Thv. Lindeman and Henrik Bull in Norway and 
J. T. Cunningham in England. Most of the work has been done by 
the Norwegians ; as a matter of fact, only one important paper, that 
of Cunningham, has been found, in any language other than Nor- 
wegian, as shown by the list of references at the end of this paper. 

NATURE OF DISINTEGRATION OF NETS. 
MECHANICAL WEAR AND TEAR. 

Before considering the various treatments that are given nets to 
prolong their usefulness, it may be profitable to consider the nature 
of the wear and tear that ruins nets. Obviously mechanical wear is 
one of the great enemies of nets. The threads rub against one an- 
other, against the gunwales of the boat, and against the floats and 



4 U. S. BUREAU OF FISHERIES. 

leads; this rubbing slowlj' abrades the threads and wears them out. 
Actual breakage by being caught on snags or hj the struggles of 
large fish and the like must be reckoned with; such breakings, of 
course, become more numerous when the net becomes weaker by rot- 
ting. A factor in the destruction of nets that is sometimes over- 
looked may also be mentioned here : That when the threads are coated 
with thick tars and the like the total weight of the net is greatlj'' 
increased and the preservative action of the tar is thus in part neu- 
tralized, the pull of the extra weight being added to other strains 
that may break the threads. 

BACTERIAL DECOMPOSITION. 

But of more importance than mechanical wear and tear in shorten- 
ing the life of nets is the action — chemical in nature — of water and 
air, aided by other agencies, particularly bacteria, in causing a weak- 
ening and rotting of the fibers. This rotting deserves very careful 
study, for it destroys nets long before they would otherwise be 
destroyed by mechanical wear and tear, and its nature, while exceed- 
ingly complex, must be understood, at least in part, before remedial 
measures can be taken intelligently. 

Up to this point chemistry has made some progress, and some 
valuable work has been done on the chemistry of preserving mate- 
rials, but as a whole the fishing industry has never taken very 
kindly to chemistry, and most of the work that bears useful fruit 
for the net preserver has been incidental to work in other important 
fields — the tanning of leather, bacteriology, and textile science. We 
must admit frankly that we know very little directly about the inti- 
mate nature of the rotting of nets. 

In the discussion of bacterial decomposition let it be assumed that 
cotton nets are being considered, because it is chiefly nets of this 
material that need preserving. They consist of fine fibers of almost 
pure cellulose, a substance very close to starch in composition, differ- 
ing from it chiefly in being insoluble in water under all ordinary 
conditions, while starch, by simple treatment, may be made to dis- 
solve. Cellulose can be made soluble in different liquids by severe 
chemical treatments. As bacteria are also capable of dissolving or 
rotting the fibers some detailed consideration will be given to their 
mode of action. 

Bacteria are plants, so very srriall that they can be seen only by 
the aid of a microscope ; they are not provided with many parts, as 
are the large plants of our acquaintance, as they have no roots, leaves, 
bark, or flowers; they are simple little rods or spheres, movable, 
reproducing under favorable conditions with the greatest rapidity. 
They have no claws, mouth, jaws, teeth, or any other offensive 
w^eapons. How, then, do they do the great damages that they are 
accused of? In a most interesting and important way. We know 
that land plants take nourishment from the ground and air by im- 
bibing it and that they have no mouths or offensive weapons. So 
do bacteria, by absorbing or soaking up the food on which they live. 
But anything to be absorbed must first be made liquid: solids can 
not be soaked up, and it happens that very few natural foods are 
liquid. So the bacterium must secrete a digestive juice that causes 



PEESERVATTOX OF FTSH NETS. 5 

the solid food surrounding it to liquefy, whereupon the liquid food 
is absorbed. This digestive juice acts in a way similar to that of the 
human digestive juice, and for the same purpose; the principal dif- 
ference between our own digestion and that of bacteria is that ours 
takes place inside our bodies after the food is taken in, while the 
bacteria digest it before. So after all there is nothing incredible 
about it. Most bacteria are equipped for using a particular class of 
foods — they are meat eaters, sugar eaters, starch eaters, fat eaters — 
and they do not mix foods. They are able to secrete a digestive 
juice capable of liquefying that particular food on which they live. 

Now, from what has been said, it is easy to see that the damage 
done to nets by bacteria must be done in either one of two ways, viz, 
the digestive juice itself or some of the changed products of digestion 
must attack the nets or else the waste products thrown off from the 
bacteria themselves (and some of these are active or virulent chemi- 
cals) must do so. If the digestive juices attack the cellulose fibers of 
the net, of course the fibers are dissolved, and this dissolution would 
be a very effective rotting. At any rate, what has already been said 
constitutes about all that can confidently be said about the intimate 
nature of bacterial decomposition of nets. If any more is to be 
known about it, a study must be undertaken. 

For preserving nets against bacteria a number of possibilities sug- 
gest themselves. Since bacteria require water for activity, it is plain 
that if we keep the nets dry as much as possible we lessen the de- 
composition. But since the use of fish nets requires them to be wet, 
another step may be taken against the bacteria. It is possible to 
impregnate the fibers with substances that are poisonous to bacteria, 
or, quite as effective, which spoil the activity of the digestive juices 
produced by bacteria. Creosote and substances containing copper 
have been used for this purpose. Another method of preventing the 
destructive action of bacteria is to make the fibers insoluble and 
proof against the digestive action of bacteria. For hardening the 
fibers and making them harmful and indigestible to bacteria, tanning 
barks and extracts, such as birch bark, catechu, quebracho, quercitron, 
etc., have been used. These Avill be considered in detail later. Mean- 
while other methods of resisting the action of bacteria are to cover 
the fibers with a protective coating, such as tar, linseed oil, etc. 

OXIDATION. 

Another enemy to nets is oxidation. The air consists of one-fifth 
oxygen, a colorless gas, which supports all fire and also is the active 
constituent of our breath. When one "sets fire to" a combustible 
material one so heats a small part of the material that the oxygen 
of the air combines directly with it. This combining releases more 
heat, which in turn hastens the combining of more oxygen with still 
more of the material, and so on, until the material is burning. While 
most combustible substances either burn rapidly or not at all, some 
things may oxidize slowly. For example, when nets are stored wet, 
covered with herring oil, l^lood, and slime, all of which are easily 
oxidizable, the oxygen of the air combines with these fish residues 
and probably also with the net. A heating thus begins, and the nets 
may even take fire; if not, the heat generated may be sufficient to 
weaken or destroy them. 



6 U. S. BUREAU OF FISHERIES. 

To prevent this oxidation it may be sufficient to coat the nets with 
a covering like tar or linseed oil; it is, however, probable that tan- 
ning the fibers makes the fibers less likely to heat. The pimple pre- 
caution of washing the nets clean and drying them while spread out 
is usually sufficient to prevent damage from overheating. 

It is further possible that the products formed by the decomposi- 
tion of fish slime and oil are injurious to nets. 

Scarcely any treatment will confine itself to preventing any one 
of the attacks on nets mentioned above, but should be directed toward 
prevention of all causes of disintegration. The successful process 
must (a) destroy bacteria or prevent their action, {b) make the 
threads insoluble and proof against the digestive action of bacteria, 
and (c) prevent oxidation by coating the fibers or making them 
proof against oxidation. 

COLORING OF NETS. 

Before consideration is given to net-preserving materials, another 
purpose of curing nets should be mentioned. When nets are treated 
or cured, their color is usually changed, and it is argued that a less 
conspicuous net is less likely to frighten away fish. This is a dis- 
puted point (see Jessen, 1910),'' though it might seem per^fectly 
natural that an invisible or poorly visible net v\'ould be less likely to 
frighten fish. It must be remembered, however, that a fish does not 
see through human eyes but through fish eyes and that a color that 
is conspicuous to our eyes might not be readily discerned by a fish. 
The French sardine fishermen use (at least they did several years ago) 
a combination of soap and bluestone that imparted a bright green 
color to the nets ; it was claimed that these caught more fish than nets 
not dyed. The Norwegians have a word, " fiskelig,''^ that they apply 
to nets that are good catchers of fish. Bluestone is applied to nets 
(by methods to be mentioned later) to make them flskelig hy mak- 
ing them bluish green. This is done, of course, on the assumption 
that if the net is in color similar to sea water the fish can not see it 
well and so do not avoid it. 

Many scientific investigations have been conducted to determine 
whether fishes can distinguish colors or not. Most of the evidence 
goes to show that the}'^ can; but perhaps they can see fewer colors 
than humans can. Some investigators have secured evidence that 
fishes do not distinguish color but that they get different amounts 
of light from different colors. Thus, a briglit green would give more 
light, or appear lighter in shade, than a dark red, though a fish could 
get no effect of greenness or of redness. It is also possible, even 
probable, that different kinds of fish have different abilities to see 
colors. Thus, it is argued, light does not penetrate very deep into 
water, and so fishes living at some depth could not see colored ob- 
jects, even if they had eyes equipped for color vision; and, since 
nature does not commonly provide useless organs or powers, color 
vision is not among the accomplishments of bottom-living fishes. 

"Author's name, with year mentioned in parenthesis, refers to the "Citation of Liter- 
ature" at the end of this paper. For example: .lessen (1910) refers to the. paper by 
Peter Jessen,, published in 1910, a reference to which will be found at the end of this 
paper. 



PRESERVATION OF FISH NETS. 7 

But it is not necessary to go further into this disputed subject. It 
stands to reason that fish perceive differences of brightness, and 
probably of color, and that if we make a net similar to sea water in 
both shade and color it will not be so readily visible. Those who 
might wish to go into this subject are referred to the article by 
Reeves (1919). 

PRESERVATION OF NETS BY TANNING MATERIALS. 

The materials most widely used for curing nets are tanning ma- 
terials — barks of birch, oak, spruce, hemlock; extracts of bark or 
wood, such as catechu, quercitron, quebracho, and the like. For pre- 
serving, the original process consisted of immersing or soaking the 
net in a decoction of bark, or in a solution of the extract. One of the 
earliest methods was the so-called " cold-tanning," a slow process 
described by Aase (1912) . This writer says that the old Norse fisher- 
men used the same nets over and over for from 30 to 50 years. He 
also says that Avhile much of this superiority of their nets might be 
explained by the fact that their thread was selected and spun by hand, 
and therefore better than modern machine-spun threads, the differ- 
ence between those times and the present, when one is lucky to use a 
net for from 3 to 10 years, is too great to be explained by the home- 
spun theory. He accounts for the difference by the cold-tanning 
process, described as follows : 

COLD TANNING. 

Every net owner had his own hirge tanning vessel, which provided a place 
for both bark and net. In this vat was placed as much water as there was use 
for, and to every barrel of water was added li vog (1 vog=36 pounds) of birch 
bark, well broken up. This was allowed to stand four or Ave weeks, but was 
daily stirred around with a stick so that it could not become thick and slimy. 
The nets were put into this mixture. In the bottom of the vat a hole was pro- 
vided so that the finished liquor could be tapped into a tub and poured back over 
the net to cover thoroughly the upper part of the net which otherwise might 
not come under the bark. The net remained in this vat two or three days, and 
every day the liquor was poured over it several times. 

Such a barking gives little color, but makes the net hard. To produce the 
desired color it must not go into the bark a single time only. Nay, it must be 
dried and again laid in the tan vessel if there is any bark left, as many as 
four or five times. After it is dried it is dipped into the sea, and it now takes 
on its right color for the first time — a color it will hold for years. If the barking 
is repeated every year the net becomes harder and harder as it grows older. 

The method takes a long time, and demands nuich labor ; when more and 
greater nets began to be used, and prices of birch bark also rose, other methods 
of barking began to be tried. 

HOT TANNING. 

The next step in the development of processes of net curing was 
the employment of a warm barking. The bark is boiled, and the 
nets are treated in the hot decoction. Aase is authority for the state- 
ment that " with this method of tanning the net acquires color and 
hardness with one treatment, and much time can by this method be 
saved. But experience has shown that warm tanning does not endure, 
by a great deal, so long as cold tanning." 



8 U. S. BUREAU OF FISHERIES. 

Then the extract, catechu, came into use. This extract is not so 
bulky, is readily sohible in water, and has been used successfully. The 
methods as practiced varied greatly, the variations being apparently 
not based on any particular reason. In general, the exfJi'act is dis- 
solved in water — 1 pound of catechu to from 1 to 3 gallons of hot 
water — and applied to the nets. 

Nets preserved with tanning extracts are brown or tan in color and 
are more resistant to deca}^ than untreated nets, as will be seen in 
figures to be given later. The tan, however, washes out, and it is 
necessary to repeat the treatment often. 

CHEMISTRY OF TANNING MATERIALS. 

Before going further with the methods of curing nets with tanning 
materials, it will be necessary to consider the chemistry of the latter. 

It is not improbable that the treatment of nets by tanning was in- 
duced by the success of the treatment of animal skins by such ma- 
terials to make leather. Tanning materials are bark or other parts 
of various trees which produce a reddish or brownish solution when 
steeped in cold water. There is scarcely a tree or shrub in some 
part of which tanning substances arre not found. 

The action of those materials may be illustrated by their effect on 
leather. Untanned hide when boiled for some time is nearly all 
dissolved; after it has been treated with tan liquor it is scarcely 
affected by boiling. When untanned hide is left in a moist condi- 
tion for some time it putrefies; tanned hide does not. Thus a hide 
that is soluble in boiling water and putrefies in cold water is con- 
verted by tanning into a hide which is neither dissolved in hot water 
nor putrescible in cold. Just how these great differences are brought 
about can be illustrated by the effect of tanning materials on gelatin 
or glue. If a tanning extract be added to a solution of gelatin, the 
latter is coagulated and precipitated and is made permanently in- 
soluble. Pure untreated gelatin readily swells in cold and dissolves 
in warm water and easily decomposes if left wet. But this tanned 
precipitate is resistant to the action of water and does not decom- 
pose. How is this important change brought about? The answer 
is given by a pair of balances. If we weigh a dry piece of gelatin, 
dissolve it, precipitate or curdle it with tan liquor, collect the pre- 
cipitate or curd, wash, dry, and weigh it, we find that it has increased 
in weight. It can also be shown that the tan liquor has lost as much 
weight as the gelatin has gained — something from the tan liquor 
combined permanently with the gelatin to make the latter insoluble 
and resistant to change. This something is called tannin. It would 
be more correct to say these somethings, for there are several tannins, 
all closely akin, all affecting gelatin in the same way. It is they 
that, acting on hides, convert the soluble, putrescible gelatins in 
hides into insoluble substance, causing the hides to become leather. 

The earlier method of analyzing tanning materials was to treat 
the solution with gelatin. This was done by taking first a definite 
volume of the solution and evaporating it to dryness and weighing 
the dry residue; then a like volume was taken from a sample that 
had been treated with gelatin, evaporated to dryness, and weighed. 
The sample that had been treated with gelatin had lost weight. The 



PRESERVATIOlSr OF FISH NETS. 9 

loss represents, of course, the substance taken up by the gelatin or 
tannin. 

Since to the leather tanner the chief item of interest is the amount 
of substance actually taken up by hides, gelatin, as a measure of the 
tanning power of materials, has been supplanted by hide powder, 
which is clean oxhide dried and ground in a suitable mill. The 
liquor is drawn through this, and the difference in the weight of 
dried residue is noted and recorded as tannin. Account is also 
taken of the difference between weights of the liquor and dried resi- 
due, this difference representing water. There is also given the per- 
centage of matter that does not dissolve in cold water, but which was 
filtered off of the liquor. Thus an analj'^sis of a tanning material 
intended to represent its value for leather tanning gives four figures, 
of which the following is a typical example (Cunningham, 1902) 
of Burmah cutch or catechu : 

Per cent. 

Tannins 46. 6 

Nontannins 20. 

Insoluble 11. 5 

Water 21. 9 

Total 100. 

There are some very significant differences between the treat- 
ment given to hides in making leather and that given to nets to 
preserve them and in the behavior of the treated materials. Hides, 
once they have taken up tannins, never let go, even though they 
are boiled or soaked in water; nets, however, lose their tanning 
materials rapidly in water, so that they must be tanned repeatedly 
if the method used for treating them is the same as that used for 
treating leather. It is thus obvious that the tannin does not com- 
bine in nets with any gelatin or other similar substance, but rather 
is merely deposited in the fibers. There is another important dif- 
ference : Hicles are tanned in a cold decoction of tan bark or ex- 
tract, while nets are usually treated in hot liquors. 

When catechu, for example, is dissolved in cold water, there 
always remains a residue, which appears in the analysis given 
above, as " insoluble." If the solution is heated to boiling, nearly 
all of this apparently insoluble material dissolves, only some pieces 
of leaves, sticks, and sand remaining. If the liquor is cooled off, 
the insoluble material again separates from solution. There is 
thus a comparatively large amount of substance insoluble in 
cold water but soluble in hot water. Upon examination, this sub- 
stance, catechin, is found to be an active tanning material, and for 
the purpose of net preserving is better than that which is soluble 
in cold water, because it will not dissolve out in use. Cunning- 
ham tried to fix the tannin in nets by first impregnating them with 
glue (which is crude gelatin) and then treating them with catechu. 
The effort resulted in failure, apparently because the glue did not 
penetrate the fibers. 

The coloring matters in barks and extracts are independent of 
the tannins and have no tanning power. Pure tannin (gallotannic 
acid from nut galls) is a light grayish yellow flaky powder, easily 
soluble in water. 

14862°— 21 2 



10 



U. S. BUREAU OF FISHERIES. 



Since the value of tanning material for net preservation depends 
upon the abundance of tannins, analyses should support important 
purchases. The following are analyses made of different samples 
of catechu, or cutch, by Cunningham, using the hide-powdcr method : 



Burmah. 



Tuan. 



Mudah. 



Caller 
Herrin. 



Tannins per cent. . 

Nontannins do 

Insoluble do 

Water do 

Total do.... 

Strength after exposure pounds; ounces.. 

Strength after exposure kilograms. 



46.6 
20.0 
11.5 
21.9 



100.0 



5;C 
2.437 



17.1 
27.1 



8;0 
3.629 



45.2 

15.0 

4.8 

34.4 



100.0 



2; 4 
.904 



50. S 

14.9 

2.2 

32.1 



100.0 



2; 9 
1.161 



It is seen from the above table that there is a considerable differ- 
ence between the values of the various samples of catechu, a fact 
equally true of other tanning extracts. The last two figures under 
each sample (which the writer has given also in kilograms for con- 
venience in comparing with the Norwegian figures that are to follow 
later) represent breaking strength. Cunningham explains as follows 
how these figures were obtained : 

In order to test the actual preserving power of different samples of cutch, 
I adopted, in my investigations in Cornwall, the following method : I procured 
a machine for testing the strength of a net before and after the experiments. 
The principal part of such a machine, which is called a dynamometer, is of 
the nature of a spring balance. One mesh of the net is attached to the balance, 
the other at a certain distance to a hook or Ivuob which can be pur.ed away 
gradually by turning a handle. As the strain increases the hand on the dial 
of the balance indicates in pounds and ounces the weight which is equal to the 
strain until one of the meshes brealis, when the hand shows the number of 
pounds equal to the breaking strain. 

In comparing the value of the different materials or processes of curing, I 
took pieces cut from the same net, and, therefore, when new, of the same 
strength, cured them, then fastened them by mooring at the bottom of Newlyn 
Harbor. After they had been under water a certain time the pieces were taken 
up and tested on the dynamometer and found to be of very different strengths, 
which showed the differences in the preserving properties of the various mate- 
rials or processes. 

One of the earliest experiments carried out on this method proves the pre- 
serving power of that part of cutch which is insoluble in cold water. So far 
as I know, there is no natural cutch or tanning extract which is completely 
soluble in cold water for the very good reason that the cutch or extract is 
generally made by boiling. But some of the red cutches put upon the market 
by the Borneo companies are almost entirely soluble in the cold, either because 
they have been chemically treated or because the insoluble part has been re- 
moved from them. 

In this experiment I tested four kinds of cutch [as above]. The last three 
were red or mangrove cutches from Borneo. In every case the strength of the 
solution used was 1 pound to 1 gallon of water, the net was dipped twice, being 
left half an hour in the liquor each time and dried between the two dips. The 
pieces of cured net were left under water, uncovered only at low water in spring 
tides, for five weeks, and then tested. 

Further reference to the table above will show that the Caller-Her- 
rin catechu which contained the highest percentage of tannin was 
one of the poorest in preserving power where the nets were actually 
exposed for a long time to water and tested for strength. The 
Tuan catechu was best, though it contained the greatest percentage 



PRESERVATION OF FISH NETS. 



11 



of insoluble matter, which would ordinarily be considered objec- 
tionable. This fact shows that the insoluble matter may add greatly 
to the value of the catechu. The reason for this superiority has 
already been mentioned. The analysis is made by dissolving sam- 
ples of material in cold water. That which does not dissolve in 
cold water is recorded as insoluble and is useless to the leather tanner. 
But a great part of this insoluble matter is readily soluble in hot 
Avater, and, inasmuch as the nets are treated in the hot solution, this 
matter is deposited in the fibers and stays in the nets while the cold- 
water-soluble tannins wash out when the nets are put to use. 

It will thus appear that analysis of tanning extracts made for the 
leather tanner's purpose is not all that could be wished from the 
fisherman's point of view. Cunningham recommends that for the 
use of net preservers there be included in the usual analysis a figure 
representing the amount of tannins insoluble in cold but soluble in 
hot water. 

It might prove to be profitable for chemical manufacturers to go 
a step further than this by separating commercial catechu into two 
parts, the cold-water-soluble part suitable for the leather industry, 
and the hot-water-soluble part, not suitable for leather tanning, but 
preferable for the preservation of fishing gear. 

With the provision that the hot- water-soluble tannins be considered 
in making calculations, Henrik Bull's (1912) point may be regarded 
as important; that is, that when tanning extracts are bought by the 
pound without reference to their content of active tannins, very un- 
profitable purchases may be made. Thus, if a sample of catechu sells 
for $0,10 per pound, and contains 40 per cent tannins, the actual price 
we pay for tannin is 10/40, or $0.25 per pound. Further, as will be 
seen from the following table, the cheaper grades of catechu may 
(but do not necessarily) furnish tannin at a price considerably higher 
than would be paid for actual tannin in more expensive grades of 
extract.** 



Samplr. 


Price per 
pound. 


Percentage 
tannin 
present. 


Price tan- 
nin per 
pound. 


A 


$0.09 
.10 
.11 
.12 


35 
45 
55 

05 


SO 26 


B 


22 


C 


20 


D 


185 







To calculate the actual cost of tannin where an analysis is avail- 
cost of extract per pound 



able, use the formula : 



Cost of tannin per pounds 



percentage of tannin in extract 



that is, divide the cost of extract per pound by the percentage of 
tannin in the extract, and the quotient represents the cost per pound 
of the tannin. 



" The original tablo is in Norwegian 0re per kilogram of extract. Since, liowever, tiie 
talile is only intended to represent a comparison, the writer has assumed suitable figures 
for American readers. 



12 U. S. BUREAU OF FISHERIES. 

. TANNING MATERIALS USED FOR FISH NETS. 

Up to this i>oint attention has been given to catechu. There are 
numerous other tanning materials put upon the market ^as bark or 
wood or as extract. The extract may be liquid, solid, in lumps, or in 
a fine powder prepared by a recently developed process. The prin- 
cipal tanning materials, as given by Cunningham, are : 

Oak bark, the bark of the common English oak, is largely used for tanning 
leather. The barks of another species in Turkey, and of the chestnut oak 
(Qucrcus castaneu) of America are also used. The bark is stripped from the 
trees when they are about 15 years old. 

Hemlock bark is really the bark of a kind of pine abundant in America, 
called Canadian pine (Abies canadensis). It is the principal tanning mate- 
rial of the United States. The extract of this material in liquid form has 
been recommended for net curing under the name of Canada cutch, and is sold 
in tins containing about 3 pounds weight. 

Mimosa, or wattle bark, is obtained from various Mimosse or acacia trees 
growing in Australia, where this is the staple tanning material. 

Quebracho is obtained from several kinds of South American trees. It is 
imported largely in the form of both dry and liquid extracts. 

Valonia consists, not of the bark, but of the cups of the acorns of a certain 
oak (Quercus wgylops) growing in the I>evant. 

Sumach consists of the leaves of a plant dried and ground. The plant grows 
in the south of Europe. 

Gambler, or terra japonica, is a dry exti'act prepared from the leaves and 
twigs of a tree called Uncaria gamhier in the Malay Peninsula. It is imported 
from Singapore. There are two forms, block gambler, in large masses, and 
cube gambler, in small, light-yellow cubes. It is not much used for net curing, 
but I believe has been used in former times at some places, such as Clovelly, 
under the name of catechu. 

True cutch, or catechu, is a dry extract made from the wood of a tree called 
Acacia catechu, which grows in India and Burmah. It may be distinguished 
as Burmah cutch, as its manufacture is carried on chiefly by natives, according 
to their own traditional methods, in Burmah. It is imported from Rangoon. 
Until recently it was used everywhere aroiuid the British coasts for net curing, 
and was used in far larger quantities than any other tanning material. 

Red cutch or mangrove cutch is made from the bark of mangrove trees, 
which grow in swamps at the mouths of rivers in tropical countries. This 
cutch is now manufactured extensively by two British companies in Borneo, 
and is largely used for net curing, having replaced Burmah cutch to a consid- 
erable extent. 

Myrobalans, divi-divi, and algarobilla are raw materials consisting of the 
dried fruits or seed pods of different trees. They are imported for use in the 
leather industry, but are not used for net curing. Canaigre is also a raw 
material, consisting of the root of a plant growing in New Mexico and Arizona, 
not used for the fishing industry. 

To this list should be added quercitron, a large timber oak {Quer- 
cus velutina) of the eastern United States, having foliage resembling 
that of the red oak, but with yellow inner bark. It is on the market 
as rough bark, rossed bark, ground bark, and solid and liquid 
extracts. As will be seen later, Bull found this to be one of the best 
materials for curing nets. 

It is thus seen that there are a great many tanning materials, that 
in common they have tannin, and that this tannin in some way pre- 
vents rotting of nets, probably by destroying the digestives with 
which the bacteria seek to rot the net, or by making the thread 
indigestible. At any rate, actual measurements of strength show 
that tannins do preserve nets, and that the principal objections to 
them as ideal preservatives are that if used unaided they wash out of 
the nets, and that if the preservation is to last the application must be 
often repeated. 



PKESERVATION OF FISH NETS. 13 

FIXING OR MORDANTING OF TANNED NETS. 

The next step, therefore, is to cause the preserving tannin to stay 
in the net, and to do this it is necessary to know something of the 
chemistry of the tannins. It has already been shown that tannins 
combine with gehitin to form a permanently insoluble substance, 
this combination being the essential principle in converting hides 
into leather. Gelatin exists naturally in hides, but there is nothing 
naturally occurring in cotton corresponding to gelatin with which 
the tamiin can form an insoluble compound. 

Tannin is readily oxidized ; that is to say, it readily takes up and 
Eombines with the oxygen of the air, and when so combined is in- 
soluble and much darker in color. AVhy, then, does not the tannin 
oxidize and stay in nets? In fact it does, to a certain extent, as any 
fisherman who has used " barked " nets knows the nets never regain 
their original whiteness. But the oxidation takes time, and in prac- 
tice the net is put into the water before much of the tannin is 
oxidized, whereupon the unoxidized tannin promptly w^ashes out. 
To store the net for a time after barking would do little good, for 
in a dry condition the oxidation proceeds very slowly or not at all. 
Repeated wetting and drying was credited by Bull in his comments 
on the paper by Aase referred to above, with the eventual thorough 
impregnation of nets by the old-time, cold-barking method. It is 
probable that by holding the nets wet for a long time after barking 
and allowing free access of air the tan might be fixed permanently 
in the fibers. 

There is, however, no need to do this, for once the chemistry of 
the process is understood the same end may be achieved by quicker 
chemical means. There are a number of chemicals which contain 
oxygen in large quantities, and which yield up this oxygen easily. 
One such chemical is potassium bichromate. If a solution of potas- 
sium bichromate be added to a solution of catechu, a dark-colored, 
insoluble compound is formed — the combination of tannin with 
oxygen, the oxygen coming from the potassium bichromate. Ad- 
vantage is taken of this principle in dyeing; catechu or some other 
natural wood dye is applied to the fibers and then darkened and 
fixed by a solution of potassium bichromate. This process is used 
primarily in the leather and textile industries for the coloring it 
gives, but no modification is needed to use the method for preserving 
nets. 

The bichromate acts not only on the tannins that are soluble in 
cold water, but upon the catechin that is soluble in hot water. 

The oxidation of tannins is greatly accelerated by alkalis — lye, 
soda, potash, etc. — but these all have a very objectionable character- 
istic in that they cause to dissolve in cold water the tanning sub- 
stance which in its natural state is soluble only in hot water. These 
alkalis are therefore not used. 

Cunningham's experiments. 

The very thorough work done by Bull in Norway and Cunning- 
ham in England has made it possible to preserve nets at much less 



14 U. S. BUREAU OF FISHERIES. 

labor and expense by use of potassium bichromate. To quote Cun- 
ningham : 

Accordingly I made at Newlyn a large number of experiments * * * to 
test wliether by the use of bichromate the net could be preserved more suc- 
cessfully or more cheaply, and the results were very favorable. One of the 
most striking of these experiments was made entirely with Burnuih cutch, of 
the Double Eagle brand. The pieces of net used were cut from the net made at 
Bridport, 25 rows to the yard, 12-ply cotton. The strength of the net when 
tested new and uncured, or " white," was 15* pounds * * *. Four pieces of 
net, cured with and without bichromate, as shown below, were put down in 
Newlyn Harbor on .January 31, 1900, and taken up and tested on March 3, so 
that they were in the water between four and five weeks. The strengths given 
are the averages of five trials on the testing machine : 

Pounds. Ounces. 

1. Dipped once in Burmah cutch, 1 pound to 1 gallon of water_ 4 2 

2. Dipped tirice in Burmah cutch of same strength, dried after 

first dip 6 5 

3. Dipped once in Burmah cutch, same strength, with 1 ounce 

bichromate potash added to 1 gallon cutch liquor 5 8 

4. Dipped once in Burmah cutch, same strength, then dipped 

separately in hot solution of bichromate, one-half pound 

to 1 gallon water 14 5 

It will be seen that of these four pieces of net, which were placed in the 
harbor at the same time, fastened to the same piece of rope, three were prac- 
tically rotten, while the fourth was nearly as strong as when new, and this 
fourth piece was the one that had been cured with bichromate of potash. 

Dipping twice in cutch alone (No, 2) seems to improve the net 
very little. Experiment No. 3 shows that the bichromate does no 
good if added to the cutch solution, but must be applied separately 
to be effective. The reason for this, as will be seen above, is that 
the bichromate makes the tannins insoluble, so that they do not get 
into the fibers at all. 

The bichromate solution used above was strong. 

The following series of tests shows the results with weaker bichro- 
mate solution, and different combinations, nets submerged January 
31, taken up March 30, put down again May 14, finally taken up and 
tested May 28 : 

Pounds. Ounces. 

1. Burmah cutch, 1 pound to gallon, net put in hot liquid and 

left to soak 24 hours 4 14 

2. Mangrove cutch A, a somewhat insoluble kind ; same treat- 

ment 5 12 

3. Mangrove cutch B, another brand ; same treatment 7 6 

4. Burmah cutch, same treatment ; net then dipped in hot 

bichromate, 1 ounce to 1 gallon water 13 5 

5. Mangrove cutch A, same treatment, following by hot 

bichromate, same strength 14 9 

6. Mangrove cutch B, same treatment, followed by hot 

bichromate, same strength 13 5 

7. Mangrove cutch B, 1 pound, with 1 ounce bichromate, 

boiled together in 1 gallon water, net left to soak 

24 hour.s 1 13 

S. Burmah cutch, 1 pound, with 1 ounce washing soda, boiled 

together in 1 gallon water, net left to soak 24 hours 6 12 

9. Mangrove cutch A and soda; same treatment 4 2 

10. Burmah cutch, 1 pound to 1 gallon sea water instead of 

fresh 5 13 

11. Mangrove cutch A, in sea water; same strength 6 5 

Here, again, it is shown that no treatment appears to do much 
good without the after treatment with bichromate. The use of 



PRESERVATION OF FISH NETS. 15 

bichromate with the cutch destroys any preserving power the cutch 
alone may have. The small differences between the different varieties 
of cutch and the different modes of handling, exclusive of the 
bichromate after treatment, are not significant. 

The following is another series of experiments made by Cunning- 
ham in which quebracho and cube gambier were tried : 

The pieces in this case were left in the harbor from May 28 to July 15, a 
period of seven weeks. The pieces of net were cut from another new net, which 
seems to have been of better quality than that previously used, as the pieces 
cured with cutch alone were not so weak after exposure as in previous experi- 
ments : 

Pounds. Ounces. 

1. Mangrove B, alone, 1 pound to 1 gallon water, dipped once, 

soaked 10 minutes 12 5 

2. Quebracho alone, same strength, same treatment 9 5 

3. Cube gambier alone, same strength, same treatment 5 

4. Mangrove B, as before, then dipped in hot bichromate, 1 ounce 

to 1 gallon water 13 8 

5. Quebracho as before, followed by bichromate, 1 ounce to 1 8 

gallon 12 14 

6. Gambier as before, followed by bicromate, 1 ounce to 1 gallon 11 5 

7. Mangrove B, 1 pound, soda 1 ounce to 1 gallon water, net dipped 

in mixture then dipped in bichromate, 1 ounce to 1 gallon 

water 7 8 

8. Gambier with soda, then bichromate in above propoi'tions 7 12 

9. Mangrove B, one-half pound to one-half gallon water, mixed 

with one-half pint bichromate solution, 1 ounce to 1 gal. on 7 8 

10. Quebracho mixed with bichromate, same proportions 10 10 

11. Quebracho, one-half pound, bichromate one-half ounce to 1 

gallon water, together 5 10 

Again, it is shown that bichromate, if used as a separate after- 
treatment, greatly increases the preserving effect of the tanning mate- 
rials ; it also further confirms the conclusion that bichromate mixed 
with the tanning material does harm rather than good. Soda added 
to the tanning extract previous to use is rather, harmful than other- 
wise, as shown by trials Nos. 7 and 8. 

lindeman's experiments. 

Thv, Lindeman (1897), in the prize-winning paper submitted in 
competition before the Trondhjem Fishery Society in 1896 for the 
best paper on preservation of nets, seems to have been first to use the 
dynamometer, or breaking-test, method of studying the preservation 
of nets. On two kinds of thread, hemp and cotton, he tried 12 pre- 
serving materials in comparison with untreated thread, as follows : 

I. Thread, without treatment. 

II. Bluestone.— li kilos (3.8 pounds) bluestone, 1 barrel water. Net lies in 
this 1 day, washed out without drying, and then put directly into the 
sea. 

III. Catechu with mordant. — To 7* kilos (16.2 pounds) net, take 1 to \\ kilos 

(2.2 to 2.75 pounds) catechu, which is boiled until dissolved; add 60 
grams (2 ounces) bluestone. The net is put in this bath while it is 
warm (60° C. or 140° F.) and allowed to stand over night. The next 
day it is well drained and brought into a bath (80° C. or 176° F.) in 
which is dissolved 180 grams (6.4 ounces) potassium bichromate. 

IV. Catechu with linseed oil. — The net is prepared according to III, dried by 

artificial drying, and brought into warmed raw linseed oil, in which it 
lies until next day ; it is then taken out, freed as much as possible 
from the oil, and dried in air. 



16 U. S. BUREAU OF FISHERIES. 

V. Birch bark, cold. — 20 kilos (44 pounds) birch bark is added to 1 barrel 
water; to this is added 1 to 2 kilos (2.2 to 4.4 pounds) of soda. This 
stands cold about 8 days to extract. The net lies in this 1 to 2 days. 
VI. Linseed oil, raw. — The net is first artificially warmed ; it is^then laid in 
raw linseed oil for 1 day. It Is then taken out, freed of oil, and dried 
as in IV. 
VII. Spruce cones. — To one-half barrel of water a quarter of cones is taken. 
This is boiled vigorously about 3 hours. After it is cooled off the net 
lies in it about 2 days. 
VIII. Wood tar, Norwegian. — The net is artificially dried as in VI, laid under 
warm wood tar for a sufficient time to assure that it is thoroiighly 
penetrated, after which it is taken out and freed of excess. 
IX. Quebracho wood. — 10 kilos (22 pounds) to about 1.50 liters (40 gallons) 
water, boiled for 1 hour, after which the net is laid in it while it is 
still warm and allowed to lie in it a couple of days. 
X. Zinc chloride. — 1 kilo (2.2 pounds) zinc chloride to 100 liters (30 gallons) 
water ; net is allowed to lie in this 1 day. 

Before treatment a series of trials was made on different places in the skein 
of thread used. The results of these stretching tests were as follows : 



A. Hemp. 



B. Cotton. 



Average breaking load. 

Weight per meter 

Breaking length 



14. 9 kilos (av. of 13 tests). 
0.623 gram. 
Zi.9 kilometers. 



8.6 kilos (av. of 10 tests). 
0.494 gram. 
17.1 kilometers. 



It will be observed that in addition to the breaking load, Linde- 
man also gives the weight per meter of the thread and " breaking 
length." This latter figure denotes the length of thread that will 
hold itself up, or the length of thread in a ball whose weight is the 
breaking load. The strength of tliread as ordinarily understood 
means strength for a given size or weight, for of course a thread can 
be made of any strength if it is only large enough. The smaller and 
lighter a thread of given strength, the better. This figure, breaking 
length, probably furnishes a better basis, if proper precautions are 
taken, than breaking load, of the quality of a net. Since the weight 
of a meter of thread is given and the breaking load is given, the 
breaking load divided by the weight of a meter will give the break- 
ing length in meters (1 kilometerr=l,000 meters, or 0.6 mile). 

This breaking-length figure is particularly valuable in judging 
such preservatives as tar and linseed oil, preservatives that add con- 
siderable weight to the net. This figure may go to show that w^here 
a net must support its own weight, one that appears to be well pre- 
served may be, in fact, poorly preserved because of the greatly in- 
creased weight. 

After testing the original thread, Lindeman treated different 
samples by the methods described above, and put them, along with 
untreated samples, in the sea, and after varying lengths of time meas- 
ured strength and weight. 

The nets were put in the sea October 6 (1895). 

First test, 8 days afterward. 

Second test, February 1 (1896), after about 14 weeks. 

Third test, May 3, about 13 weeks after .'second test. After the third test the 
samples were destroyed by a passing boat. A new series was prepared and 
hung out in the sea July 7. 

Fourth test, October 1 (1897), after 12i weeks. 

Fifth test, January 1 (1897), after 13 weeks. 



PRESEEVATIOIN' OF FISH NETS. 



IT 



The test pieces taken up October 1 were covered with mussel spat, 
and were greatly reduced in strength. By the time the fifth test was 
made the nets had so far disintegrated that they could not be tested 
on the dynamometer ; the investigator therefore made notes with the 
letters, «, 6, and c to indicate how^ far gone they were, meaning some- 
thing like poor, poorer, poorest. 

It is apparent that the pieces of net used for the fourth and fifth 
tests underwent decomposition much more rapidly than the earlier 
ones. While Lindeman offers no explanation of this difference, it 
may be readily explained by the warm weather, since it is common 
experience that nets rot more rapidly in warm weather than in cold. 

The results of these tests are summarized in the accompanying 
table. Each figure represents an average of from 5 to 13 trials, so 
that differences in particular places on the thread are ironed out to 
some extent. 



strength and weight of thread . 



Without 
prepara- 
tion. 



Blue- 
stone. 



III. 

Catechu 

with 
mordant. 



IV. . 
Catechu 

with 
linseed 

oil. 



V. 



Birch 
bark. 



A. HEMP. 

Test 1: 

Breaking load kilogram. . 

Weight per meter gram. . 

Breaking length kilometer. . 

Test 2 : 

Breaking load kilogram. . 

Weight per meter gram. . 

Breaking length kilometer. . 

Test 3: 

Breaking load kilogram. . 

Weight per meter gram. . 

Breaking length kilometer. . 

Test 4: 

Breaking load kilogram . . 

Weight per meter gram.*. 

Breaking length kilometer. . 

Test 5: 

Breaking load kilogram. . 

Weight per meter gram. . 

Breaking length kilometer. . 

B. COTTON. 

Test 1: 

Breaking load kilogram. . 

Weight per meter gram . . 

Breaking length kilometer. . 

Test 2 : 

Breaking load kilogram. . 

Weight per meter gram. . 

BreaMnglength kilometer. . 

Test 3: 

Breaking load kilogram . . 

Weight per meter gram. . 

Brealdng length kilometer. . 

Test 4: 

Breakingload kilogram- . 

Weight per meter gram. . 

Brealdng length kilometer. . 

Test 5: 

Breakingload kilogram. . 

Weight per meter gram,. . 

Breaking length kilometer. . 



13.3 
.600 
22.2 

8.6 
.554 
15.7 

6.4 
.509 
12.5 



.558 
13.9 



.3 
.530 

4.4 



12.6 
.675 
18.7 

11.2 
.593 
18.9 

11.8 
.646 
18.3 

9.0 
.804 
11.2 



C) 



13.7 



19.7 



.723 
16.8 

12.1 
.687 
17.6 



765 
11.9 



10.9 
.910 
12.0 

14.0 
1.000 
14.0 

13.2 
.837 
15.8 



1.200 
6.6 



7.5 
1.045 



8.2 
.507 
16.1 



.493 
15.6 

7.0 

.564 
12.8 



.489 
5.5 



(0 



7.9 


5.6 


.566 


.961 


13.9 


5.8 


8.5 


7.5 


.610 


.894 


13.9 


8.4 


9.3 


7.4 


.610 


.865 


15.2 


8.5 


6.7 


7.1 


.580 


.822 


11.5 


8.6 


5.8 


6.3 


.570 


.764 


10.2 


8.2 



11.5 

.628 
18.3 

9.1 

.660 
13.8 



.652 
14.9 



732 
6.3 



('■) 



.538 
14.5 

6.1 
.530 
11.5 

3.8 
.577 
6.6 

2.8 
.536 
5.2 



(0 



Note.— a, 6, and c, meaning something like poor, poorer, poorest,indicate that nets had disintegrated too 
far to be tested on the dynamometer. 

14862°— 21 3 



18 



U. S. BUREAU OF FISHERIES. 



Strength and weight of thread. 



A. HEMP. 

Testl: 

Breaking load kilogram . 

Weight per meter gram. 

Breaking length kilometer. 

Test 2: 

Breaking load kilogram. 

"Weight per meter gram. 

Breaking length kilometer. 

Test 3: 

Breaking load kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 4: 

Breakingload kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 5: 

Breaking'load kilogram. 

Weight per meter gram . 

Breaking length kilometer. 

p.. COTTON. 

Test 1: 

Breaking load kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 2: 

Breakingload kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 3: 

Breaking load .kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 4: 

Breaking load kilogram. 

Weight per meter gram. 

Breaking length kilometer. 

Test 5: 

Breaking load kilogram. 

Weight per meter gram. 

Breaking length kilometer. 



VI. 

Linseed 

oil. 



12.6 
.S21 
15.3 



.704 
16.3 

12.9 
.642 
20.1 

7.8 
.S40 
9.3 



(O 



9.6 

8.4 
.734 
11.4 



.710 

12.0 

tl.O 
.660 
9.1 



VII. 
Spruce 
cones. 



13.4 
.852 
15.7 

12.4 

.67S 
18.3 

12.6 
.712 
17.8 



700 
5.0 



(*>) 



(0 



.585 
14.5 

8.0 
.571 
15.1 

8.5 
. 000 
14.1 



.510 
7.3 



W 



VIII. 
Tar. 



10.9 

13.1 
.958 
13.7 

11.9 
.792 
15. 

9.3 
1.030 
9.0 



('■') 



7.8 
.974 
8.0 

7.6 

.848 
S.8 



.830 
10.1 

6.8 
.856 
7.9 



IX. 

bracho. 



.720 
17.4 

11.9 
.686 
17.3 



.803 
15.8 

5.0 
.738 
6.8 



C) 



(«) 



8.1 
.559 
14.5 

8.2 
.564 
14.6 

8.1 
.590 
13.7 

2.9 
.495 
5.9 



(6) 



X. 

Zinc 

chloride. 



11.4 
.679 
16. S 

8.1 
.588 
13.8 

6.6 
.622 
10.6 



7.2 
.647 
14.0 

3.0 

.487 
6.2 

2.9 
.523 
5.5 



Of the methods that depend on tannins for their activity, Nos. Ill, 
IV, V, VII, and IX, only two may be considered at all successful; 
they are Nos. Ill and IV. These two received identical treatment — 
i. e., catechu with copper sulphate and potassium bichromate — but 
No. IV received a subsequent treatment with linseed oil. If judged 
by the breaking strength alone, the linseed oil adds a very little ; but 
it judged by breaking length, it is not so good as the previous one. 

Of methods of tanning nets this is additional evidence that the use 
of a fixer or mordant, potassium bichromate, greatly increases the 
preserving quality of tanning materials. 

The use of zinc chloride suggested itself to Lindeman because it 
converts cellulose into so-called hydrocellulobe and is used as a pre- 
servative for railroad crossties. It is a failure for preserving nets. 

The nontannin preserving materials will be considered later. 

Another point about the table worthy of notice is that tannins 
have an effect on hemp nets similar to that on cotton, but not so great. 

It should also be noted that Lindeman's paper appeared five years 
earlier than Cunningham's paper, or that of Bull, next to be con- 
sidered. 



preservation of fish nets. 19 

bull's experiments. 

Bull (1901), in Norway, carried on a similar series of experiments, 
using a greater number of combinations, including oak bark, quer- 
citron extract, and coal tar. He also carried out more elaborate 
processes of prex)aration, including such manipulations as three or 
four baths and combinations of second treatments. The table follow- 
ing gives Bull's results and carries brief descriptions of the methods 
used. In the text Bull says he barked the nets in " the customary 
way." 

Lindeman used the bluestone (or copper sulphate, copper vitriol, 
blue vitriol, as it is variously called) in the same bath with the 
tanning material. On this point Bull (1901) says: 

When I began this investigation, since I used quercitron extract in as pure a 
condition as was obtainable, in lieu of catechu, I observed that in solution in 
water it has, with copper-vitriol solution, a reaction that produces a precipitate 
which dissolves with difficulty in water, for which reason the coloring method 
must be regarded as disadvantageous, because the precipitate is formed rather 
on the thread and is not in the solution. In addition, I found that the second 
bath may be also harmful in the use of very warm (80° C. or 176° F.) solution 
of potassium bichromate, since this strong agent, with the high tempei-ature 
used, may very well cause a weakening of the thread. 

Bull also says : 

As a barking material quercitron extract has shown itself to be the best. 
* * * A noteworthy result is shown in experiment 17, in which the net is 
barked twice with quercitron extract and afterwards treated with the oxidati(m 
mixture. It is shown that the net, after 11 weeks, is of the same strength as 
before it was immersed in the sea, namely, 23 kilograms. 

Quercitron, as well as other tanning extracts and barks, can be 
secured from American dealers in tanners' supplies. 

The copper may have some preserving action ; Cunningham thinks 
it is injurious. It appears to the writer that, while it may strengthen 
the defense against certain organisms, its chief use on nets is to 
impart a dark, durable color. 



20 



U. S. BUREAU OF FISHERIES. 





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22 n. S. BITREATT OF FISHERIES. 

Lime may also be used as a mordant or fixer for the tanning ma- 
terial. The lime is applied in the form of a solution as follows : Add 
slacked lime to water in a large container, and let stand with occa- 
sional stirring for several days. The clear liquor that rernains after 
the excess lime has settled is to be applied to the nets in lieu of the 
potassium-bichromate-and-bluestone solution in the method to be 
given below, after they have been barked. No measurements of the 
strength of nets so preserved have been found. 

A rather elaborate process of tanning employing lime fixation is 
described in an article in Norsk Fiskeritidende (1886). A transla- 
tion of this article by Herman Jacobson was published in the Bulle- 
tin of the United States Fish Commission (Vol. VI, No. 7, June 12, 
1886, pp. 97-104). The method consists of three applications of 
catechu, one of lime water, and a final treatment of a mixture of 
Stockholm (pine) tar and coal tar. That method appears to be too 
elaborate for use in the fisheries of to-day. A point of value in this 
paper, however, is that where more than one bath of the tanning ex- 
tract is used the first one should be much weaker than the others. 

IMPROVED RECIPE FOR TANNING NETS. 

This section of the paper, treating preservation by tanning ma- 
terials, is to be concluded with a recipe regarded as the best, and a 
summary. The recipe, given by Bull (1902), is: 

To 220 pounds of net (cotton or hemp, the method is best suited to cotton) 
take 33 pounds of solid extract of quercitron, or 143 pounds of oak bark. (Cate- 
chu does not give such good r,esults, but if used, take 53 pounds.) 

The extract is boiled <» until dissolved in 130 gallons of water. Stir con- 
tinuously in the vessel to prevent the extract from burning to the bottom ; the 
warm solution is poured over the net, which is laid in the vessel. With a flat 
board, if necessary, push the net down under the liquor. Cover the vessel well 
with a tarpaulin or sail canvas so that it can cool oft only very slowly. After 
the vessel is completely cooled off the net is taken out and as much of the water 
as possible is wrung out before beginning the after treatment. If this is done 
at once, without preliminary drying, some of the tannin will dissolve out and 
the net will lose. 

The after treatment is carried out as follows: To 220 pounds of net take 
2i pounds bluestone and 3^ pounds potassium bichromate, and dissolve them 
in 1")0 gallons of cold water.^ After the substances are entirely dissolved and 
the whole stirred well, the net is put into the bath. It is best to move the net 
about in the liquid from time to time so that it works evenly on the entire net. 
In this bath the color of the net is much darkened ; if quercitron is used a 
uniform brown color is produced, like that of a barked net that has been used 
a long time. After two hours the net is taken out. 

It is the safest plan now to wash the net in water— for example, by putting 
it in a tub — but perhaps this is not necessary, so it can be spread out at once to 
dry, or be taken aboard. The water from the after treatment is quite worth- 
less, for the salts added have been completely used up. 

By way of comment it may be remarked that the best way to dis- 
solve the extract is to put it in a coarse ba^ and to suspend the bag 
in hot water. This prevents debris from going into the solution. lu 
heating the large amount of water the exhaust steam from an engine, 
or any other steam of a pound or two pressure may be used. 

" The advisability of boiling the tan liquor is disputed. It appears the safer procedure 
to heat the water during the process of dissolution of the extract to about 17.^>° F. 
(80° C). 

" Bluestone attacks metal vessels, and it should, therefore, be dissolved in l)arrels or 
other wooden vessels. 



PRESERVATION OF FISH NETS. 



23 




■":|0((;y 




24 U. S. BUREAU OF FISHERIES. 

The accompanying drawing (Barclay, 19056) represents a plant as 
used in Scotland for barking nets. Catechu or other extract is dis- 
solved in tank B^ whicli is heated by steam from a stearg pipe. A 
system of pipes, the arrangement of which is obvious in the drawing, 
l^rovides for drawing off the liquor into tanks where the nets are 
treated. D is a steam injector or siphon used for convenience in 
transferring the liquor from one vat to another, or returning it to 
the dissolving tank. 

It is assumed in these recipes that the nets are perfectly clean and 
free from oil before tanning. Preferably, nets should be tanned be- 
fore they are ever used. Ii they are dirty or greasy they should be 
washed in warm water and soap, well rinsed in warm water, and 
dried before tanning. 

It Avill be noticed from Bull's figures that a double treatment of 
quercitron extract before mordanting (experiment No. 17) gave best 
results. If it is desired to do this — and this procedure is recom- 
mended — the first tan should be much weaker than the second ; that is, 
use half the total amount of quercitron for first bath, add the remain- 
ing half to the same liquor for second bath, following with mordant, 
or after treatment. The net should be dried between first two baths 
of quercitron. This procedure is in keeping with the practice in the 
leather-tanning industry. 

While this method is usually referred to in the literature as " Ball's 
method," it should be stated that an after treatment with a chromate 
(sodium chromate) was used before; for example, mention was made 
of it in the article in the Allgemeine Fischerei-Zeitung (1896) re- 
ferred to, and potassium bichromate in combination with catechu 
was tested by Lindeman (189T). Olaus Tysk0, in a paper submitted 
in the Trondhjem contest, states that the method using catechu, copper 
sulphate, and potassium bichromate had been " used in Fosen for the 
last 20 years." (Konserveringsmidlers indflydelse paa fiskegarn- 
straad. TillaGg til Arsberetning for 1898 fra Trondhjems fiskerisel- 
skab, pp. 4r-1.) 

SUMMARY OF METHODS OF PRESERVATION OF NETS BY TANNING. 

1. Tanning methods are suitable for preservation of nets, leave the 
nets soft and pliable, and afford a high degree of protection. 

2. Very little increased protection is afforded by treating tanned 
nets with lineseed oil or tar. 

3. An after treatment of potassium bichromate following the ap- 
plication of tan liquor greatly increases the preserving power of tan- 
ning materials, such as quercitron, catechu, gambier, etc. 

4. Copper sulphate (bluestone, copper vitriol) contributes to the 
color of nets when used as an adjunct to tanning methods, but does 
not add much, if anything, to the protecting power of the tanning 
material. 

5. So far as the data go, hemp threads are protected by tanning 
materials just as is cotton, but not such a great degree of protection 
is afforded. 

6. No data have been found regarding the preservation of linen 
thread. 



PRESERVATION OF FISH NETS. 25 

7. All the methods of tanning impart a dark color to the nets, 
which color may be advantageous in making the nets less conspicu- 
ous in the water. 

PRESERVATION OF NETS BY METHODS NOT DEPENDENT ON 
TANNING MATERIALS. 

The methods of prolonging the life of nets which make no use of 
tanning materials, or make use of them only as adjuncts, employ 
linseed oil, pine tar, coal tar, bluestone, soap and bluestone, salt, 
smoke, and creosote. 

Of these, linseed oil and tars are physical protections to the net; 
they fill up the spaces between the fibers and to a large extent keep 
the water from coming into contact with the materials of which the 
threads are composed. Naturally these materials are very efficacious, 
but that there are many and serious objections to the general use of 
linseed oil and tar will appear later. Linseed oil will be considered 
first. 

LINSEED OIL. 

For practical purposes the animal and vegetable oils are looked 
upon as being divided into two principal groups, the nondrying oils 
and the drying oils. The nondrying oils, of which coconut, peanut, 
cottonseed, and olive oils are examples, are used for soaps, foods, 
lubricants, and the like ; they do not " dry " ; that is, they do not 
form a skin upon being exposed to air, but under storage conditions 
may become rancid. The drying oils, such as linseed and men- 
haden oil, when exposed to air " dry " ; that is, they form tough, 
somewhat elastic skins, which, when a pigment is incorporated with 
them, constitute paints. The conspicuous properties of these oils, 
that is, the turning rancid of the first class, and the drying to a skin 
of the second, are both traceable to the same cause — oxidation, or 
absorption of oxygen from the air. Both classes possess a keen 
appetite for oxygen, and the process of absorption is attended with 
the generation of heat; if the oil is distributed in such a way that 
great surface is offered for oxidation and at the same time little 
opportunity is afforded for the heat to escape, so much heat will be 
generated as to start a fire, as it is well known that oily rags will do, 
and also nets. Another peculiarity about this heating is that the 
hotter the rags or nets become, the faster the oxidation. 

Linseed oil is the great drying oil, used the world over as the body 
for paints. It has been used in Holland (Barclay, 1904) for many 
years for preserving nets and to a considerable extent in the same 
way in England, particularly at Lowestoft and Yarmouth. This 
method, according to Cunningham, is simple : The nets are given one 
bath of catechu, thoroughly dried ; and then one bath of linseed oil, 
drained, and dried. After drying, which takes two or three weeks 
or more, they are again bathed in catechu, which removes any 
undried oil. In use they are occasionally given a treatment of 
catechu, like any other net. The method, as used by the Dutch, 
according to Jessen (1903), is as follows: 

Any grease on the net is first removed in water, to which a little more than 
2 quarts of slacked lime is added, per barrel of water. The net is then thor- 
oughly dried, and introduced into a bath of 18 pounds catechu to 35 gallons of 
water ; the water is boiled and stirred till the catechu is dissolved. The liquor 



26 U. S. BUREAU OF FISHERIES. 

is kept hot while the net is put into it. It is left in until the knots have had 
time to be thoroughly penetrated; then taken out, drained, and the moist net 
packed in a vessel till next morning, vi^hen it is taken out and dried very 
thoroughly. As soon as completely dry it is ready to receive the same treat- 
ment again, and so on until it has had 6 to 8 treatments, between ^cli two of 
which it is thoroughly dried out, care being taken that the interior of knots is 
soaked at each treatment and dried with each drying. 

The net, perfectly dried, is now brought under raw linseed oil — 1 pound of 
oil for each pound of net. Tlie oil is kept as cold as possible. The excess of 
oil is drained off in a vessel with a false bottom. This done, the net is laid out 
in a field to dry, which drying takes two or three weeks or more. Much rain 
will injui-e the net, but under no circumstances should the net ever be heaped 
up until absolutely dry, even if it does rain. If it is heaped up it is certain 
to lieat, and, aside from the danger of fire, it may be ruined by the heat 
generated. 

There is no doubt that this is an excellent preserving method for 
nets and deserves all the esteem in which it has been held for so many- 
years. But, because of its laboriousness and the present cost of linseed 
oil, it is not at all likely to receive consideration under present con- 
ditions in the United States. Neither is it every fisherman that has 
idle land on which he can lay out nets for three weeks or more to dry. 
Nor is the method necessary in many cases, for if the figures by 
Lindeman and Bull, given above, are reliable, the threads may be 
as well preserved by catechu or other tan, followed by a mordant, 
at much less cost and labor. The threads of hemp, preserved with 
catechu and mordant, were reduced in strength from 13.7 to 12.1 
between first and third tests (28 weeks) ; preserved with catechu, 
mordanted, and then oiled, the figures are 10.9 and 13.2, or an ap- 
parent increase in strength. With cotton the results were similar, 
only both appeared to become stronger. But it will be noticed that 
the oiled nets are 50 per cent or more heavier than the other and the 
breaking length is correspondingly shorter. 

Nets oiled with linseed oil are stiff er and harder than nets not oiled ; 
in some cases, such as the gill nets for shad, this would be a serious 
objection; but for nets that stay constantly in the w^ater, such as 
trammel or moored nets, oiling might be well justified. Cunningham 
said he left oiled nets in the water two months and found no diminu- 
tion in strength in that time. Barclay (1905) concludes that im- 
proved tanning methods are good where there is opportunity for 
occasional drying of nets, but where there is no opportunity for 
drying it may be desirable to oil the nets after they are tanned or 
"barked." 

TAR. 

Preservation of nets by tar is the principal method used in the 
United States. The nets are simply passed through hot tar, freed 
from excess, and partially dried. On use the drying continues until 
the tar is hard and tough. Of this method Cunningham says : 

This method of treating a net is very cheap and tested by the method above 
described — breaking tests — on pieces of net exposed in a harbor, the preserva- 
tion is very perfect. A piece of net lost scarcely any strength after two months in 
the water, and, moreover, a tarred net is distinctly stronger tlian a cutched 
net, because the dry tar increases the strength of the cotton fibers by gluing 
them together. As an antidote to putrefaction coal tar is perfect, no septic 
organisms being able to live in it. The fibers of the cotton, being covered by 
the tar, do not come actually into contact with water. For these reasons tar 
is an excellent preservative for coarse nets for rough use, such as trawl nets. 



PRESERVATION OF FISH NETS. 27 

But for d»ift nets there are many objections to its use in the manner considered. 
The net is too rigid and stiflC, and, tlierefore, does not usually mesh the fish 
well although to some extent the net is made more flexible by occasional dips 
in hot cutcli, which softens the tar and removes a portion of it. The rigidity 
of the net causes it to wear out mechanically ; after two or three years it is 
apt to give way at the knots, owing to the breaking of the stiffened fibers under 
the constant bending. 

Another method sometimes used employs cutch and tar together, 
the tar being stirred into the hot cjitch and the net bathed in the 
mixture. Cunningham found this to be very little better than the 
cutch or catechu alone, for the reason that the tar does not mix 
uniformly with the cutch, but breaks up into little droplets which 
attach themselves to the threads. The threads are therefore not 
uniformly protected by the tar. 

Tar consists of two parts, a liquid part which is separately 
known as creosote, and a black, solid part which is left behind when 
the creosote evaporates. When the tar is first applied both are 
present, but as time passes the liquid creosote gradually evaporates, 
while the solid part remains. Both assist in protecting the nets, 
the solid by gluing the fibers together, the liquid by killing bacte- 
ria; one protects, the other preserves. 

If in the table given by Bull (p. 20) the samples prepared with 
tar are compared with samples prepared in other ways, it is seen 
that tar holds its own against all rivals, if we consider preserva- 
tion of breaking strength only. But it is noticed that weight is 
increased from around 1.6 grams per 10 meters to around 3.5, 
or about 2^ times; the breaking length is correspondingly reduced, 
while the absorption of water is reduced from about 250 per cent 
to about 50 per cent ; that is, the amount of water the threads will 
absorb is reduced by the application of tar from about 2^ times its 
own weight to one-half its own weight. 

The added weight of tar is a very material disadvantage in large 
nets, for it increases the labor of handling nets and prolongs the 
time of every move of the net. On the other hand. Bull's table shows 
that the tarred net soaks up much less water than the barked net 
and that, since absorbed water adds to the weight of the net just 
as tar does, the weight added by water must also be considered. 

In the case of drift nets, where the poise of the net in the water 
is of greatest importance, the balance of the net has a bearing on 
the method of barking (Jessen, 1906). Jessen argues thus: A 
quantity of sea water of the same air and salt content and at the 
same temperature as that of the sea, will neither sink nor float, 
but will stay at whatever depth it is put, and when water thus 
soaks into a net it will tend neither to sink nor float the net, but 
is a dead weight. This dead weight, however, must be counter- 
balanced by a greater weight on the lead line than would be needed 
Avithout it ; that is, the weights on a water-logged net must be greater 
by an amount equal to the weight of the water in the net in order 
to keep the net vertical. Thus, if the untreated net in Bull's table 
took up 227 per cent water (No. 1) and required 24 kilograms 
stone sinkers, the barked net which took up 179 per cent water 
(No. 11) would require 21.6 kilograms sinkers, and with the barked 
and tarred net (No. 23) that took up 54 per cent of water, only 
10.5 kilograms sinkers would be needed, and that with lead sinkers 



28 U. S. BUREAU OF FISHEKIES. 

these figures are 14.6, 13.2, and 6.4 kilograms, respectively. Then, 
to show the practical force of his argument, he points out that with 
the untreated net (No. 1) with stone sinkers one must work with 
the weight of the net, 8.6 kilograms plus the water soaked up, 19.5 
kilograms plus the stone sinkers, 24 kilograms, or 52.1 1k;ilograms 
all together. While with the barked and tarred net and lead sink- 
ers these weights are, net, tanning material and tar, 15.7 kilograms ; 
absorbed water, 8.5 plus the necessary lead, 0.4 kilogram; a total 
of 30.6 kilograms. He also shows that the first net, requiring 17 
men to handle it, can, if its weight is reduced by barking and 
tarring, be handled by only 10 men. No argument is required to 
show, also, that of two nets made of material exactly the same 
size and quality, but one weighted down to nearly twice the weight 
of the other, the heavier will wear faster than the lighter. While 
space does not permit of an extended review of the discussion of 
these matters," it should be pointed out that Jessen appears to 
have overlooked the fact that if a tarred net of a weight of 3.15 
increases in weight by 54 per cent, it will weigh 4.85 in all, while 
the untreated net of 1.45 will, when increased by 227 per cent, weigh 
4.95, or more than the tarred one. Bull, in the article referred to 
in the footnote, gives the correct mathematics for making the cal- 
culations. 

Cunningham's further experiments. 

At this point it is appropriate to introduce the remaining experi- 
ments conducted by Cunningham, using all the ordinary net preserv- 
atives in various ways. 

PKia'ARATION OF SAMPLES. 

1. Cutch alone (one-half pound cutch boiled in one-half gallon of water). — 
The pieces of net put in this until well soaked, then dried. Then put into cutch 
of same strength, steeped for two days, then dried. 

2. Cutch and glue (one-half pound glue dissolved in 1 gallon of water). — ^The 
net dipped into this, then squeezed and put into hot cutcli — one-half pound cutch 
to one-half gallon of water — then dried. Afterwards dipped a second time into 
cutch of same strength and dried again. 

3. Cutch, glue, and bichromate of potash. — The net was dipped into glue, 
1 pound to one-half gallon of water, with a little bichromate of potash added ; 
then put into cold cutch and left to steep two days. 

4. Cutch and copper sulphate. — The net was steeped two days in cutch, one- 
half pound to one-half gallon of water, then, while wet, put into copper sul- 
phate, 1 pound to one-half gallon of water, and after a short soak rinsed in 
fresh water and dried. 

5. Cutch and coal tar. — The net was first saturated with coal tar, then squeezed 
and wrung out several times with hot water, then dried for a week, and after- 
wards dipped in hot cutch, one-half pound to one-half gallon of water. 

6. Cutch and coal tar mixed. — One-half pound cutch boiled in one-half gallon 
of water and then about a pint of coal tar stirred into the hot solution. The 
net was dipped into the hot mixture, then dried. 

7. Cutch, tar. and green oil [a creosote distilled from coal tar]. — The net was 
first steeped three days in cutch, one-half pound to one-half gallon of water. 
Then the same cutch was heated and the net passed hot from this through a mix- 
ture of coal tar, Stockholm [pine] tar, and green oil as thick as paint. The net 
was then passed through a wringing machine and dried. 

"See further, Bull (1906). Reference is made by Bull to a discussion of the matter 
between Dr. Johan Hjort and Peter Jessen in the Bergens Tidende, presumably in 1906. 



PRESERVATION OF FISH NETS. 



29 



S. Coal tar and green oil mixed. — The net was steeped in the mixture, then 
passed through a wringing machine, and hung up to dry. 

9. Cutch and green oil. — The net was steeped several days in cutch, one-half 
pound to one-half gallon of water, then dried and put into green oil, then passed 
through a wringing machine and hung up to dry. 

10. Green oil alone. — The net was simply saturated with green oil, passed 
through a wringer, and hung up to dry. 

11. Cutch and Stockholm tar, mixed (one-half pound. cutch boiled in one-half 
gallon of water, and one-half pint Stockholm tar stirred into the hot solution). — ■ 
The net dipped into the mixture, squeezed out. and dried. 

12. Cutch, Stockholm tar, and green oil.— The net was steeped three days in 
cutch, one-half pound to one-half gallon of water, then dried and soaked in 
Stockholm tar warmed, with a little turpentine added. As the net was very 
hard and sticky, it was soaked with green oil and passed through the wringing 
machine. 

13. Cutch and linseed oil. — The net was steeped in cutch (one-half pound 
to one-half gallon of water) for three days, dried, and then dipped in boiled oil, 
with driers added. After some weeks it was dipped again in cutch and dried. 

14. Soap and copper sulphate (one-half pound soap boiled in one-half gallon of 
water). — The net soaked in this and then put into a solution of copper sulphate, 
one-half pound to one-half gallon of water. 

15. Soap, copper sulphate and linseed oil. — The net, prepared as in 14, was 
saturated with boiled oil, with driers added, and hung up to dry. 

The pieces were all cut from the same mackerel net, 24^ rows to 
the yard. 12-ply, and the following table shows the results of testing : 



Mode of cure. 



Strength when 
dry. 



Strength after 

4 weeks in 

water. 



Strength after 

2 months in 

water. 



Cutch only, two dips and steeped 

Glue and cutch, one dip in glue, two in cutch 

Cutch, glue, and bichromate of potash 

Cutch and copper sulphate 

Cutch and coal tar, tarred first , 

Cutch and coal tar, mixed 

Cutch, tar, and green oil, passed direct from the 

cutch into the tar 

Coal tar and green oil, mixed 

Cutch and green oil •- 

. Green oil alone 

. Cutch and Stockholm tar mixed 

. Cutch, Stockholm tar, and green oil 

. Cutch and linseed oil 

Soap and copper sulphate 

. Soap, copper sulphate, and linseed oil 



Lhs. 
15 
17 
16 
13 
18 
17 

17 
16 
15 
16 
17 
14 
15 
15 
15 



nzs. 

9 

2 
11 

8 

4 
12 

3 


14 

5 
13 

4 

1 

1 

1 



Us. 
16 
9 
14 
10 
21 
18 

18 
16 
18 
16 
17 
18 
16 
15 
15 



Lbs. 
6 



It is evident that Cunningham did not carry his tests far enough 
to give decisive indications. In spite of this insufficiency, it is plain 
that those methods are good which depend on tar or oil as a protec- 
tive covering, where these substances really cover, but when they are 
broken up into tiny particles or applied to a wet net, as in Nos. 6, 7, 
and 11, little protection is given. 



SHRINKAGE CAUSED BY PEESERVING. 



Cunningham also kept a record of the shrinkage caused by the 
various methods of curing nets. As stated above, the nets were 24^ 
rows per yard before treatment. After treatment they varied ac- 
cording to the following list. (Of course, the greater the number 
of rows there are the more the shrinkage that has taken place.) 



30 



U. S. BUREAU OF FISHERIES. 



No. Rows per yard. 

10. Green oil alone 25^ 

11. Cutch and Stockholm tar 27 

12. Cutch, Stockholm tan and 

green oil 2.5^ 

13. Cutch and linseed oil 27 

14. Soap and copper sulphate 27 

15. Soap, copper sulphate, and lin- 

seed oil 27 



No. Rows per yard. 

1. Cutch only 26i 

2. Glue and cutch 25i 

3. Cutch, glue, and hichromate_ 25^ 

4. Cutch and copper sulphate 2.54 

5. Coal tai- and cutch 28^ 

G. Cutch and coal tar mixed 27 

T. Cutch. tar, and green oil 25^ 

8. Coal tar and green oil 25^ 

9. Cutch and green oil 26^ 

All the methods caused shrinkage, the greatest being caused by 
coal tar and cutch, but the other combinations of cutch and tar 
caused marked shrinkage. All the tanning methods cause shrinkage, 
and the shrinkage increases with each application of the preserva- 
tive. 

To conclude the discussion of tar as a preservative, it can be said 
that tar effects excellent preservation, is comparatively inexpensive, 
and requires much less labor and time than, for example, the com- 
bination of catechu and linseed oil. For the heavier and coarser 
kinds of nets that are anchored or moored in the water, such as tram- 
mel or pound nets or nets that are handled by machinery, the method 
is well suited. But for gill nets, the method is not at all suited, and 
for even the heavier seines that are hauled by hand, consideration 
should be given to the extra weight added by tar and the conse- 
quently increased number of men necessary to handle nets so pre- 
served. In such cases, especially for nets that can be dried occa- 
sionally, the more improved barking methods, such as quercitron and 
potassium bichromate, are likely to prove to be better and to be little 
more expensive or laborious than methods employing tar. 

Tar should never be mixed with catechu solution or anything else 
containing water before application to the net and should never be 
applied to a wet net. It may be thinned with creosote, " green oil," 
turpentine, etc., without injury. If a net be cutched or barked before 
being tarred, it should be thoroughly dried before the tar is applied. 
While tar may be applied profitably to new, white nets, it seems 
likely that it will always yield a good return on the investment to 
tan the nets with quercitron and bichromate and to follow with a 
thorough drying before application of the tar. 

CREOSOTE, SMOKE, ETC. 

As stated above, tar consists of a solid and a liquid part. The 
liquid part really consists of a number of different liquids and vola- 
tile solids, such as carbolic acid, benzol (or benzene), napthalene, etc., 
mixed, which, when separated, have different important commercial 
uses. They are distilled off from coal tar. One portion (the third 
main portion distilling over at from 230 or 240 to 270° C.) is known 
as " green oil " or creosote oil, a greenish-yellow, oily liquid, heavier 
than water, and containing various antiseptic substances. It is used 
for the preservation of crossties, fence posts, telegraph and tele- 
phone poles, and has been used for the treatment of nets. Reference 
to Cunningham's table above shows that creosote oil alone is a good 
preservative for nets and causes little shrinkage; it also possesses 
this advantage, that it does not make nets stiff. The principal objec- 
tion to its general use is that it washes out or evaporates rather rap- 



PRESERVATION OF FISH NETS. 31 

idly from the net, and no method of fixing it is known. The net is 
oily or greasy for some time after it is treated and is therefore objec- 
tionable to handle. 

Concerning the mode of application of creosote, Cunningham says : 

There are many different ways of applying tlie green oil or creosote to the 
nets; the net may be well cutched first, then dried, soaked in the green oil 
when dry, then passed through a wringing machine, and spread out to dry ; or 
the net may be passed straight from hot cutch, without drying, through the 
green oil, and then dried, or, instead of the oil alone, a mixture of tar and 
green oil may be used. In whatever way it was applied I found pieces of net 
treated with green oil had lost but very little strength after two months' 
exposure iu Newlyn Harbor. 

The principal preserving matters in creosote that comes from wood 
go over in the smoke when the wood burns in a smoldering fire. 
Upon this fact is based a method using smoke.® 

It is stated in the articles referred to that this method had been 
used on the Gulf of Courland for many years in houses that had no 
chimneys by allowing the smoke to go through passages into a loft 
where the nets were hung. A direct method of applying the smoke 
is to fasten the net to the underside of boards which are supported 
above a smoking wood fire. 

While this method appears to be primitive, there is nothing chemi- 
cally unreasonable about it, and it may be that under certain circum- 
stances the method would be applicable to-day. It would certainly 
be much better than nothing, provided the nets were not allowed to 
be overheated during the smoking process. It would be necessary to 
repeat the treatment, perhaps several times a year. The method has 
the advantage of depositing upon the fibers the volatile antiseptic 
substances of tar, without the heavy thick parts, and it would ap- 
pear less likely to shrink the nets. 

COPPER SULPHATE. • 

It was noticed in the figures of Lindeman, given above, that hemp 
threads were improved by every method that improved cotton 
threads; only one preserving material had a more marked effect on 
hemp than on cotton — that is, copper sulphate (or copper vitriol, blue- 
stone, blue vitriol, etc., as it is variously known). This substance 
has long been used for nets, alone or in combination with other sub- 
stances. According to a quotation in the Norsk Fiskeritidende 
(1906) this is used in Norway for the treatment of salmon nets. One 
kilogram (2 J pounds) of copper sulphate is dissolved in a barrel of 
water. The nets are treated with this by allowing them to lie in it 
overnight. They are put into the sea as soon as they are taken from 
the bath, without preliminary drying. Lindeman's figures show that 
the method does not deserve serious consideration. 

What is perhaps of much more importance is a method of using 
copper sulphate in combination with soap. A method of this kind is 
saicl to have been used in the French sardine industry to give the nets 
a color. Oils consist of two parts, glycerin combined with fatty acids. 
When the glycerin is taken out, and soda or potash substituted for it, 

" See Mittheilungen des Westpreussischen Fischerei-Vereins (1896), Deutscher Fischerei- 
Verein (1885), and Norsk Fiskeritidende (1896). 



32 XT. S. BUREAU OF FISHERIES. 

ordinary soaps are produced. If, instead of the alkalis, any other 
metal — such as copper, mercury, aluminum, etc. — is used, insoluble 
soaps — such as copper soap, mercury soap, aluminum soap, etc. — are 
produced. The simplest method of preparing these '' h^vy metal 
soaps " is first to make ordinary soap, then treat it in solution with 
a compound of the metal whose soap is desired. Thus, if to a solution 
of ordinary soap aluminum chloride is added, an insoluble waxy 
precipitate falls — aluminum soap; if copper sulphate is emploj^ed 
instead of aluminum chloride, a bright green, insoluble copper soap 
is formed. The insoluble calcium soap is a very familiar substance 
formed when soap is dissolved in " hard " water — a tallowy stutl 
that gets on one's hands, the bathtub, etc. This is calcium or lime 
soap, A similar soap is used for temporary calking of small leaks in 
boats ; a soap of aluminum is used to waterproof clothing, for it makes 
clothes difficult to wet, the water rolling oif " like water from a duck's 
back.^' 

Now, if the principal reason for using copper to preserve nets is 
that it kills bacteria and other injurious living things, and if the 
principal objection to its use as bluestone is that it washes out so 
readily, there will be no difficulty in seeing that the object of using ii 
in the form of a soap is to take advantage of its protective property 
and at the same time to prevent it from escaping into the water. 
Since copper soap is quite insoluble in water,, there would be no way 
to get it into the fibers if it were made before it is applied ; it is there- 
fore necessary to cause the copper soap to be produced inside the fiber 
by impregnating the threads first with soap solution and then with 
copper sulphate. In the practice of preserving nets the following 
process, according to Cunningham, is used : 

To treat a net by this process from one-half to three-fourths pound of ordi- 
nary soap, such as mottled soap * * * is used for each gallon of water, 
and tlie soap is dissolved by boiling in a copper or in a galvanized bath over a 
fire. The net is then soaked in the soap solution, taken out, squeezed through 
the hands, and allowed to drain. The copper sulphate, which is also known as 
blue vitriol or bluestone, must not be dissolved in an iron vessel, as it will at- 
tack and dissolve the iron. It nmst be put into a wooden or earthenware ves- 
sel, and it is not necessary to use heat to dissolved it, as it will dissolve in cold 
water if stirred up for a short time. The net while still hot from the soap 
solution is then passed through or put into the solution of bluestone, and the 
whole net becomes uniformly green. The net is then rinsed in cold water. 
About three-fourths pound of bluestone to a gallon of water is the proportion 
required. 

This method preserves the net, according to Cunningham's fig- 
ures, for about four weeks, but he says that after two months the 
sample treated was quite rotten. Tlie process can, of course, be re- 
peated as often as necessary, and by repeated treatments a net should 
be kept in condition for years. It causes strong shrinking of the net. 

A similar method is recommended for ropes and canvas by the 
Norsk Fiskeritidende (1887). The procedure there given is as 
follows : 

Ropes are laid first for four days in a solution of copper vitriol (20 grams 
to a liter of water — two-thirds ounce to a quart) and then dried.. They are then 
tarred in the usual way or laid in a soap solution (100 grams to a liter of 
water — 3J ounces to a quart) until they are saturated through. Canvas is 
treated only with the vitriol and soap. 



PRESERVATIOlSr OF FISH NETS. 33 

GENERAL COMMENTS. 

Only the more important and widely used or promising processes 
for the preservation of nets have been considered. To anyone who 
has searched literature it would be a surprise if a great many other 
methpds and processes were not found to have been tried. The list 
given by Jessen includes, besides barking, smoking, alum, train oils, 
tallow, grease, bluestone, potassium bichromate, various compounds 
of mercury, iron vitriol, pine tar, wood oils, coal tar, aniline dyes, 
and various other products of gas works, salt, resins, soaps, lime, etc. 
But all the recorded data found that will have a material value have 
been included in this paper. 

It should be obvious to most people that nets should always re- 
ceive some preservative treatment. Coarse nets, pound nets, and the 
like should be both barked with catechu or quercitron, mordanted 
with potassium bichromate, and then tarred. Where it is not pos- 
sible or suitable to tar the nets, they should receive the catechu or 
quercitron treatment and the mordant. It is preferable to use two 
baths of quercitron, the first containing only one-half the total 
amount to be used. 

Though no actual figures have been brought forth to prove it, 
there is little doubt that nets are destroyed more rapidly in warm 
climates and warm weather than in cold. Fishermen should take 
note of this fact and be accordingly more careful of their nets where 
the weather is warm. It is also likely that foul, dirty water works 
more rapid destruction on nets than clean water. 

One of the possible ways to avoid the disintegration of nets is, of 
course, the chance of using some material that is not subject to de- 
cay — metals, for example. A person signing the initials C. J. (1912) 
describes briefly in the Dansk Fiskeritidende some experiments with 
aluminum, brass, copper, and galvanized-iron wire for bow nets. The 
aluminum proved to be best. 

No important results have come from efforts to substitute metals 
for plant fibers for nets. 

CARE OF NETS. 

When nets are piled up wet — especially if they are foul with slime, 
blood, fat, etc. — the rapid oxidation heats the net. Even if the net 
does not take fire the heat generated may very well cause a great 
weakening. This weakening will not be visible, but will tell in a 
much shorter life of the net. However carefully the net is barked 
or tarred, a very short life can be looked for if the net has been 
heated. 

For a temporary preservative, where it is not possible to dry the 
nets, it is customary to salt them. This is a useful treatment, as far 
as it goes. Salt is not in itself poisonous or injurious to small 
organisms or bacteria (for they live in the sea which contains much 
salt) if the concentration is not too great. But it is well known that 
when any watery organism is exposed to a salt solution stronger than 
its own juice water will be extracted and usually the organism dies. 
The salt is injurious to living things not because of its saltiness, but 
because of its concentration ; not because it is poisonous, but because 



34 U. S. BUREAU OF FISHERIES. 

it extracts the water necessary for things to live on. The rule is that 
a stronger salt solution will extract water from a weaker juice where- 
ever it comes in contact with it. 

This principle is made use of in uifinj vrnys. Every tisherman 
knows that salt draws the water out of fish in the curing process. 
It is not so apparent, but it is equally true, that it draws the water 
from and kills the bacteria that would otherwise cause the fish to 
decay, and thus preserves it. Any equally concentrated substance 
would do the same. Thus sugar is used in very concentrated sirup 
to prQserve fruits; if the preserves were sufficiently diluted with 
water, bacteria could live in them and they would spoil. 

In this way salt preserves nets. It dissolves in the moisture on the 
threads to make a very strong solution; this strong solution kills 
bacteria and other small organisms by extracting the water from 
them. From this it is hardl}^ necessary to say that the salt should 
be applied generously, and preferably in the dry condition, to a wet 
net. If brine is used, it should be very strong. 

But salt will not prevent heating in an oily net that has just 
caught very fat fish, such as herring. The heating is caused by the 
air working on the fat. The only way to prevent this heating is 
either to get rid of the fat or to prevent the air from getting to it. 
Aboard a vessel it is not always convenient to wash the net out imme- 
diately, nor is there room to spread the net (if spread, the heat, of 
course, escapes as fast as produced and no harm is done). Bull 
(1905) suggests that to prevent this heating of recently used herring 
nets aboard a vessel, there be provided a wooden tank with a tight- 
fitting lid, filled with water or salt solution, and that the net be put 
into this and covered over with the lid until there is opportunity to 
wash it. The water or salt solution keeps out the air and prevents 
heating. The cheapest obtainable grade of salt may be used, since 
there is not likely to be anything in it that is injurious to nets. 

Nets, as every fisherman knows, should be washed and dried at 
every opportunity. 

CONCLUSION. 

The most important methods of preserving nets are tanning, for 
which an improved recipe is given on page 22; tarring, found on 
page 26; and creosote, found on page 30. Other methods are also 
given. 

CITATION OF LITERATURE. 

In the preparation of this paper the following publications have been con- 
sulted and matei'ial therein quote<l or reproduced here and translated where 
necessary. Those interested in pursuing the subject are referred to them for 
further details. 

Aase, Hans. 

1912. Barkning. Norsk Fiskeritidende, Side Aargang, pp. 169-172, 1912. 
Bergen. 
Barclay, M. 

1904. Barkning og Oljing af Siklegarn paa hollandsk Maade. Norsk 
Fiskeritidende, 23de Aargang, pp. 448-458, 475-485, 1904. Bergen. 
1905a. Om Barkningsmetoder. Referat fra Fiskerm0det paa Sortland den 
lite og 12te .Tuli, 1905; ved M. H. Stoltz. Norsk Fiskeritidende, 
24de Aargang, pp. 233-239 (discussion of paper, pp. 238-239), 
1905. Bei-gen. 
19056. Sildegarnenes Konservering 1 England og Skotland. Norsk Fisk- 
eritidende, 24de Aargang, pp. 372-376, 1905. Bergen. 



PRESERVATION OF FISH NETS. 35 

Bull, Henrik. 

1901. Om Barkning af Garn. Norsk Fiskeritidende, 20de Aargang, pp. 

863-872; 1901. Bergen. 

1902. Barkning af Garn, Norsk Fiskeritidende, 21de Aargang, pp. 401- 

404, 1902. Bergen. 

1905. Om Opbevaring af Garn ombord. Norsk Fiskeritidende, 24de 

Aargang, p. 207, 1905. Bergen. 

1906. Om vore Drivgarn eg deres Belastning. Norsk Fiskeritidende, 

25de Aargang, pp. 195-203, 1906. Bergen. 
1912, Hvad Slags Barkestof skal man kj0be for Barkning af Garn ? Norsk 
Fiskeritidende, 31de Aargang, pp. 39-40, 1912. Bergen. 
Cunningham, J. T. 

1902. Tlie chemistry of net-curing. Fish Trades Gazette and Poultry. 

Game and Rabbit Trades Chronicle, Vol. XX, No. 993, p. 29 ; No. 
994, p. 29 ; No. 995, p. 29 ; No. 996, p. 29 ; No. 997, p. 27 ; No. 998, 
p. 31 ; No. 999, p. 31 ; No. 1000, p. 31 ; No. 1001, p. 31 ; No. 1002, 
p. 31 ; No. 1003, p. 25 ; No. 1004, p. 27 ; No. 1005, p. 31 ; No. 1006, 
p. 31; No. 1007, p. 37; No. 1008, p. 31; No. 1009, p. 31; June- 
September, 1902. London. 
Deutscher Fischerei-Verein. 

1885. Mittel zur Conservierung von Fischnetzen. Mittheilungen der Section 

fiir Kusten und Hochseefischerei, No. 1, pp. 34-35, 1885. Berlin. 

J , C. 

1912. Fors0g med Metaltraadsnset. Dansk Fiskeritidende, N. R. lOde 

Aargang, p. 488, 1912. K0benhavn. 
Jessen, Peter. 

1903. Det hollandske Drivgarn. Norsk Fiskeritidende, 22de Aargang, 

pp. 395-407, 1903. Bergen. 
1906. Om Konservering af Garn og Not. Norsk Fiskeritidende, 25de Aar- 
gang, pp. 151-159, 1906. Bergen. 
1910. Fiskenes Farvesans og sj0farvede Garn. Norsk Fiskeritidende, 29de 
Aargang, pp. 219-222, 1910. Bergen. 
Lindeman, Thv. 

1897. Om konserveringsmidlers indflydelse pa fiskegarnstrad. Arsberet- 
ning fra Trondhjems fiskeriselskab for budgetterminen, 1st juli, 
1896-30te juni, 1897. Trondhjem. 
Mittheilungen des Westpreussischen Fischerei-Vereins. 

1896. Zur besseren Haltbarkeit der Netze. Allgemeine Fischerei-Zeitung, 
XXI .Tahrg. No. 3, pp. 44-45. 1896. Munchen. 
Norsk Fiskeritidende. 

1886. Bevaring af Garn. Noi'sk Fiskeritidende, 5te Aargang, pp. 138-151, 

1886. Bergen. (A translation by Herman Jacobson, appeared in 
the Bulletin of the U. S. Fish Commission, Vol. VI, No. 7, pp. 
96-104, 1886. Washington.) 

1887. Bevaring af Tougvserk og Seildug. Norsk Fiskeritidende, 6te Aar- 

gang, p. 295, 1887. Bergen. 

1896. Praktisk Konserveringsmiddel for N0ter og Garn. Norsk Fiskeriti- 
dende, 15de Aargang, pp. 647-648, 1896. Bergen. 

1906. Behandling of Fisken0ter med Blaasteu. Norsk Fiskeritidende, 25de 
Aargang, p. 251, 1906. Bergen. 
Reeves, Cora D. 

1919. Discrimination of light of different wave-lengths by fish. Behavior 
Monographs, Vol. 4, No. 3, 1919, Serial No. 19, 106 pp. (Bibliog- 
raphy). Cambridge, U. S. A. 

o 



